1. Field of the Invention
The present invention relates to a protection circuit, and more particularly to a protection circuit to aid in avoiding the use of an inappropriate Alternating Current (AC) power source.
2. Background of the Invention
A piece of equipment known as Automatic Test Equipment (ATE) is used for testing function of various print circuit boards (PCB). Referring to FIG. 1, a typical ATE includes a voltage transforming circuit 100 with a commutating circuit inside, a control circuit 120, a switch circuit 140 and a magnet valve 160. AC voltage from an external AC power source is transformed and commutated by the voltage transforming circuit 100 to provide a working voltage to the control circuit 120. The control circuit 120 outputs a control signal to the switch circuit 140, thereby setting the condition of the switch circuit 140 to be switched on or off. When the switch circuit 140 is on, the magnet valve 160 connects to the AC power and in turn controls other components of the ATE to test the PCB. Otherwise, the magnet valve 160 is not connected to the AC power.
Generally a magnet valve 160 functions using either 220V or 110V AC power but not both. The magnet valve 160 will perform abnormal when it is connected to an improper AC power source. For instance, a magnet valve 160 for use with a 110V AC power source will be fused when connected to a 220V AC power. Conversely, a magnet valve 160 for use with a 220V AC power source cannot function normally when connected to a 110V AC power source.
Accordingly, what is needed is a protection circuit for avoiding the use of an improper AC power source.